1. Field of the Invention
The present invention relates to a so called diaphragm making use of a property of matter so designed that an electrical or a magnetic optical element whose light transmittance pvaries under the electrical of the magnetic field is used for the diaphragm device for a single lens reflex camera with TTL light measuring system, particularly to a device for confirming the depth of focus by means of the diaphragm making use of a property of matter.
Further, the present invention relates to a device for confirming the depth of focus by means of an electromagnetic diaphragm driven with the electromagnetic force.
2. Description of the Prior Art
Until now the strength of a spring is used as the driving force for the diaphragm device for a camera, and therefore a mechanism for charging it is needed. Further, in the case where the diaphragm device is provided on the interchangeable lens, a complicated connecting mechanism of the camera body with the diaphragm device of the interchangeable lens is needed, which results in increasing cost and complexity of the camera mechanism.
Further, in the case where the conventional diaphragm device is closed for confirming the depth of focus, it is necessary to exert power against the strength of the spring, which means that considerable power is needed.
In the case of conventional automatic exposure single lens reflex cameras with priority on shutter time, the diaphragm device in the interchangeable lens is driven by releasing the charged strength at the side of the camera body, so that when the diaphragm closing confirmation operation is carried out in advance, the charged strength is released, which means that recharging becomes necessary for shutter release.
Further, when, in the case of the conventional diaphragm device, the diaphragm closing operation is once carried out, the diaphragm is closed down to the aperture value corresponding to the object brightness information before the diaphragm has been closed and the value is maintained after that. Thus, even when the object brightness varies for some reason, the aperture value is not varied, which cannot be said to be the correct aperture value.
Recently, various types of diaphragm making use of a property of matter in which the electromagnetic optical element whose light transmittance varies under an electric (or magnetic) field have been proposed for use in a camera. For use as the above mentioned electromagnetic optical elements, the Kerr cell, the transparent ferroelectric ceramic (PLZT) and the liquid crystal whose optical characteristics vary in the presence of the electrical field, the Faraday element whose optical characteristics vary in the presence of a magnetic field, the electrochromy element making use of the electrodeposition or the element making use of the electrophoresis are known. These diaphragms which make use of a property of matter have many features that the conventional mechanical diaphragm does not. Firstly, no mechanical connecting mechanism is needed so that they are compact and light. This contributes greatly to freedom in camera design. Further, there takes place no shock at the time of the diaphragm closing and the noise accompanied therewith so that it is convenient for the photographer. Further, because the diaphragm making use of a property of matter is driven by means of an electrical circuit, such diaphragm can be well adapted to the recent electronic camera and can be a large step in the realization of a totally electronic camera in the future.
Various electromagnetic diaphragms driven electromagnetically have also been proposed.
The present invention is intended to offer an aperture stop-down confirmation device for such diaphragm making use of a property of matter or electromagnetic diaphragm.